Pulse wave detection device, biological information measurement device, and control method for pulse wave detection device

ABSTRACT

A pulse wave detecting device includes a sensor section and a control unit. The sensor section is rotatable about a first axis and is rotatable about a second axis. The control unit determines a rotation angle about the first axis based on DC components of pressure detecting elements included in element rows. Then, in a state where the sensor section is controlled to the optimal pitch angle, the sensor section is pressed against the body surface, and a pulse wave is detected based on pressure signals detected by pressure detecting elements in this state, and vital information is calculated based on the detected pulse wave.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT application No.PCT/JP2017/014751, which was filed on Apr. 11, 2017 based on JapanesePatent Application (No. 2016-082068) filed on Apr. 15, 2016, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a pulse wave detecting device, a vitalinformation measuring device, a method for controlling a pulse wavedetecting device, and a control program for a pulse wave detectingdevice.

There is a known vital information measuring device capable of measuringvital information such as the pulse, the heart rate or the bloodpressure using information detected by a pressure sensor set in contactwith a surface of a living body portion where an artery such as theradial artery of the wrist passes (see Patent Literature 1).

Patent Literature 1 discloses a vital information measuring deviceincluding a drive section that rotates a pressure sensor including aplurality of element rows each including a plurality of pressuredetecting elements about an axis extending in a direction perpendicularto an arrangement direction of the plural element rows (i.e., adirection perpendicular to an artery). In this vital informationmeasuring device, maximum amplitude values of pulse waves detected bythe respective plural element rows are compared with one another torotate the pressure sensor in such a manner that the amplitude valuesaccord with one another.

Patent Literature 1: Japanese Patent Publication No. H01-288228

SUMMARY OF THE INVENTION

In order to detect an accurate pulse wave from an artery using each of aplurality of element rows arranged in a direction of extending theartery, it is preferred that the artery is pressed similarly by each ofthe plural element rows.

In the vital information measuring device described in Patent Literature1, the pressure sensor is rotated in such a manner that the maximumamplitude values of pulse waves respectively detected by the pluralelement rows accord with one another, so as to accord the pressingstates of the artery by the plural element rows with one another.

When the artery is started to be occluded on the peripheral side havinghigh resistance prior to the center side, however, a reflected wave iscaused accordingly, and the reflected wave is superimposed on a pressuresignal detected by the element row disposed on the center side, whichmay cause an error in the amplitude value of a pulse wave.

Besides, even when a reflected wave is not caused, since the pluralelement rows press different portions of a living body, there is apossibility that a difference may be caused in the attenuation factor ofthe amplitude among pulse waves detected by the respective element rowsdue to a difference in the composition of a subcutaneous tissue of thepressed portion, or the like.

The vital information measuring device described in Patent Literature 1does not take such a detection error of a pulse wave detected by aplurality of element rows into consideration.

The present invention was devised in consideration of theabove-described circumstances, and an object is to provide a pulse wavedetecting device capable improving pulse wave detection accuracy byflexibly changing a pressing state, toward a body surface, of a sensorsection pressed against the body surface for use, a vital informationmeasuring device, a control method for a pulse wave detecting device,and a control program for a pulse wave detecting device.

The pulse wave detecting device of the present invention, includes:

a sensor section that includes at least one pair of pressure detectingelements arranged in a direction perpendicular to a first direction;

a pressing section that presses the sensor section against a bodysurface of a living body in a state where the first direction crosses adirection of an artery extending below the body surface;

a rotation drive section that rotates the sensor section about an axisextending in the first direction;

a storage control section that stores, in a storage medium, pressuresignals detected by the pressure detecting elements in a state where arotation angle of the sensor section about the axis is controlled to aspecific value and the sensor section is pressed against the bodysurface by the pressing section; and

a rotation angle determining section that determines the specific valuebased on DC components of pressure signals detected, in a state wherethe sensor section is pressed against the body surface by the pressingsection, respectively by a first pressure detecting element and a secondpressure detecting element out of the pressure detecting elementsincluded in the sensor section, the first pressure detecting element andthe second pressure detecting element being different from each other ina position in the direction perpendicular to the first direction.

The vital information measuring device of the present inventionincludes: the above-described pulse wave detecting device; and a vitalinformation calculating section that calculates vital information basedon the pressure signals stored in the storage medium.

The method for controlling the pulse wave detecting device of thepresent invention, the pulse wave detecting device including: a sensorsection that includes at least one pair of pressure detecting elementsarranged in a direction perpendicular to a first direction; a pressingsection that presses the sensor section against a body surface of aliving body in a state where the first direction crosses a direction ofan artery extending below the body surface; and a rotation drive sectionthat rotates the sensor section about an axis extending in the firstdirection, the method includes:

a storage control step of storing, in a storage medium, pressure signalsdetected by the pressure detecting elements in a state where a rotationangle of the sensor section about the axis is controlled to a specificvalue and the sensor section is pressed against the body surface by thepressing section; and

a rotation angle determining step of determining the specific valuebased on DC components of pressure signals detected, in a state wherethe sensor section is pressed against the body surface by the pressingsection, respectively by a first pressure detecting element and a secondpressure detecting element out of the pressure detecting elementsincluded in the sensor section, the first pressure detecting element andthe second pressure detecting element being different from each other ina position in the direction perpendicular to the first direction.

The control program for the pulse wave detecting device of the presentinvention, the pulse wave detecting device including: a sensor sectionthat includes at least one pair of pressure detecting elements arrangedin a direction perpendicular to a first direction; a pressing sectionthat presses the sensor section against a body surface of a living bodyin a state where the first direction crosses a direction of an arteryextending below the body surface; and a rotation drive section thatrotates the sensor section about an axis extending in the firstdirection, the control program causes a computer to execute:

a storage control step of storing, in a storage medium, pressure signalsdetected by the pressure detecting elements in a state where a rotationangle of the sensor section about the axis is controlled to a specificvalue and the sensor section is pressed against the body surface by thepressing section; and

a rotation angle determining step of determining the specific valuebased on DC components of pressure signals detected, in a state wherethe sensor section is pressed against the body surface by the pressingsection, respectively by a first pressure detecting element and a secondpressure detecting element out of the pressure detecting elementsincluded in the sensor section, the first pressure detecting element andthe second pressure detecting element being different from each other ina position in the direction perpendicular to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the external structure of apulse wave detection unit 100 of a vital information measuring deviceaccording to one embodiment of the present invention.

FIG. 2 is an enlarged view of the pulse wave detection unit 100 of FIG.1.

FIG. 3 is a diagram, taken from a side of the elbow of a user, of thepulse wave detection unit 100 in a worn state illustrated in FIG. 1.

FIG. 4 is a diagram, taken from a side of a portion in contact with thewrist, of the pulse wave detection unit 100 in the worn stateillustrated in FIG. 1.

FIG. 5 is a diagram illustrating a block structure of the vitalinformation measuring device of the present embodiment excluding thepulse wave detection unit 100.

FIG. 6 is a flowchart used for explaining an operation in a continuousblood pressure measurement mode of the vital information measuringdevice of the present embodiment.

FIG. 7 is a flowchart used for explaining details of step S3 of FIG. 6.

FIG. 8 is a diagram illustrating change in a pressure signal detected bya target element positioned above the radial artery in a selectedelement row selected in step S38 of FIG. 7.

FIG. 9 is a flowchart used for explaining details of step S5 of FIG. 6.

FIGS. 10A to 10C are diagrams illustrating states where a roll angle ofthe pulse wave detection unit 100 of FIG. 1 is controlled to threevalues.

FIG. 11 is a graph illustrating a relationship between a DC level of apressure signal detected by each pressure detecting element of theselected element row in a state where the roll angle is controlled asillustrated in FIGS. 10A to 10C and the position of the pressuredetecting element.

FIG. 12 is a flowchart used for explaining details of step S8 of FIG. 6.

FIG. 13 is a diagram illustrating exemplified pressure signals detectedby a first target element and a second target element.

FIG. 14 is a diagram illustrating exemplified pressure signals detectedby the first target element and the second target element.

FIG. 15 is a flowchart used for explaining a modification of detailedprocessing of step S5 of FIG. 6.

DETAILED DESCRIPTION OF EXEMPLIFIED EMBODIMENT

An embodiment of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 is a schematic diagram illustrating an external structure of apulse wave detection unit 100 of a vital information measuring deviceaccording to one embodiment of the present invention. The vitalinformation measuring device of the present embodiment is used whileworn, with a band not shown, on a living body portion (the left wrist ofa user in an exemplified case of FIG. 1) in which an artery to bemeasured for vital information (the radial artery T in the exemplifiedcase of FIG. 1) is present.

FIG. 2 is an enlarged view of the pulse wave detection unit 100 ofFIG. 1. FIG. 3 is a diagram, taken from a side of the elbow of the user,of the pulse wave detection unit 100 in a worn state illustrated inFIG. 1. FIG. 4 is a diagram, taken from a side of a portion in contactwith the wrist, of the pulse wave detection unit 100 in the worn stateillustrated in FIG. 1. It is noted that FIGS. 1 to 4 merelyschematically illustrate the pulse wave detection unit 100, and do notlimit dimensions and arrangement of respective components.

The pulse wave detection unit 100 includes a housing 1 including an airbag 2 therein, a plate section 3 corresponding to a plate-shaped memberfixed on the air bag 3, a rotation section 5 supported on a biaxialrotation mechanism 5 a rotatably against the plate section 3 around eachof two axes, and a sensor section 6 provided on a surface of therotation section 5 on the opposite side from the plate section 3.

The air bag 2 functions, in a state where the pulse wave detection unit100 is worn on the wrist as illustrated in FIG. 1, as a pressing sectionfor pressing a pressing surface 6 b of the sensor section 6 against thebody surface of a living body portion (the wrist). The pressing sectioncan be any mechanism as long as it can press the sensor section 6against the artery, and is not limited to one using an air bag.

The air bag 2 is controlled by a pump not shown for the amount of airheld therein to move the plate section 3 fixed on the air bag 2 in adirection vertical to the surface of the plate section 3 (the surface onthe side of the rotation section 5).

In the worn state illustrated in FIG. 1, the pressing surface 6 b of thesensor section 6 included in the pulse wave detection unit 100 is incontact with the skin of the wrist of the user. In this state, theamount of air injected into the air bag 2 is increased to increase theinternal pressure of the air bag 2, and hence the sensor section 6 ispressed against the body surface. Hereinafter, the description is madeon the assumption that a pressing force applied by the sensor section 6to the body surface is equivalent to the internal pressure of the airbag 2.

As illustrated in FIG. 4, the sensor section 6 includes an element row60 including a plurality of pressure detecting elements 6 a arranged ina direction B corresponding to a first direction, and an element row 70including a plurality of pressure detecting elements 7 a arranged in thedirection B. The element row 60 and the element row 70 are arranged in adirection A perpendicular to the direction B. In the state where thepulse wave detection unit 100 is worn on the wrist, the element row 60is disposed on a peripheral side, and the element row 70 is disposed ona center side.

Every pressure detecting element 6 a forms a pair with a pressuredetecting element 7 a disposed in the same position in the direction B,and a plurality of such pairs are arranged in the direction B in thesensor section 6. As each of the pressure detecting elements 6 a and thepressure detecting elements 7 a, for example, any of a strain gaugeresistance element, a semiconductor piezoresistance element and anelectrostatic capacitance element is used.

The respective pressure detecting elements included in the element row60 and the element row 70 are formed on the same plane surface, and theplane surface is protected by a protection member of a resin or thelike. The plane surface having the pressure detecting elements thereonand the surface of the protection member protecting the plane surfaceare parallel to each other, and the surface of the protection memberforms the pressing surface 6 b.

Each of the pressure detecting elements 6 a (7 a) can detect a pressurevibration wave generated in the radial artery T and transmitted to theskin, namely, a pulse wave, when pressed against the radial artery T insuch a manner that the arrangement direction crosses the radial artery T(at substantially right angles).

A distance in the arrangement direction between the pressure detectingelements 6 a (7 a) is set to be so sufficiently small that a necessaryand sufficient number of elements can be disposed above the radialartery T. A length of the arrangement of the pressure detecting elements6 a (7 a) is set to be larger than the diameter of the radial artery Tby a necessary and sufficient size.

As illustrated in FIG. 4, the biaxial rotation mechanism 5 a is amechanism for rotating the rotation section 5 around each of a firstaxis X and a second axis Y, that is, two axes perpendicular to apressing direction of the plate section 3 by the air bag 2.

The biaxial rotation mechanism 5 a is rotatively driven by a rotationdrive section 10 described later, so as to rotate the rotation section 5around each of the first axis X and the second axis Y set on the surfaceof the plate section 3 to be perpendicular to each other.

The first axis X is an axis extending in the arrangement direction ofthe pressure detecting elements in the element row 60 or the element row70 (the direction B). The first axis X is set between (in theexemplified case of FIG. 4, in the center between) the element row 60and the element row 70 in the exemplified case of FIG. 4. The first axisX is in an arbitrary position in the direction A.

The second axis Y is an axis extending in the arrangement direction ofthe element row 60 and the element row 70 (the direction A). The secondaxis Y is set on a straight line equally dividing the element row 60 andthe element row 70 in the exemplified case of FIG. 4. The second axis Yis in an arbitrary position in the direction B.

When the rotation section 5 is rotated around the first axis X, thesensor section 6 is rotated about the first axis X. Besides, when therotation section 5 is rotated around the second axis Y, the sensorsection 6 is rotated about the second axis Y

Hereinafter, the rotation of the sensor section 6 about the first axis Xis designated as pitch rotation. Besides, a rotation angle of the sensorsection 6 about the first axis X is designated as a pitch angle.Furthermore, the rotation of the sensor section 6 about the second axisY is designated as roll rotation. Besides, a rotation angle of thesensor section 6 about the second axis Y is designated as a roll angle.

The pitch angle is defined by an angle between a plane vertical to thepressing direction and the pressing surface 6 b. In a state where thepressing surface 6 b is vertical to the pressing direction, the pitchangle is 0 (zero) degree. It is assumed that a pitch angle obtained bypitch-rotating the sensor section 6 from this state to one direction (apositive direction) out of rotatable directions has a positive value,and that a pitch angle obtained by pitch-rotating the sensor section 6in an opposite direction to the one direction (a negative direction) hasa negative value.

Hereinafter, a direction of rotating the sensor section 6 from the stateof the pitch angle of 0 (zero) degree in a direction in which theelement row 60 comes closer to the body surface (a counterclockwisedirection in FIG. 1) is defined as the positive direction of the pitchrotation, and a direction of rotating the sensor section 6 in adirection in which the element row 60 comes away from the body surface(a clockwise direction in FIG. 1) is defined as the negative directionof the pitch rotation.

The roll angle is defined by an angle between the plane vertical to thepressing direction and the pressing surface 6 b. In a state where thepressing surface 6 b is vertical to the pressing direction, the rollangle is 0 (zero) degree. It is assumed that a roll angle obtained byroll-rotating the sensor section 6 from this state to one direction (apositive direction) out of rotatable directions has a positive value,and that a roll angle obtained by roll-rotating the sensor section 6 inan opposite direction to the one direction (a negative direction) has anegative value.

Hereinafter, a direction of rotating the sensor section 6 from the stateof the roll angle of 0 (zero) degree in the counterclockwise directionin FIG. 3 is defined as the positive direction of the roll rotation, anda direction of rotating the sensor section 6 from the state of the rollangle of 0 (zero) degree in the clockwise direction is defined as thenegative direction of the roll rotation.

Each of the pitch angle and the roll angle can be controlled to aplurality of values.

FIG. 5 is a diagram illustrating a block structure of the vitalinformation measuring device of the present embodiment excluding thepulse wave detection unit 100.

The vital information measuring device includes the pulse wave detectionunit 100, the rotation drive section 10, an air bag drive section 11, acontrol unit 12 for integrally controlling the whole device, a displaysection 13, an operation section 14 and a memory 15.

The sensor section 6 of the pulse wave detection unit 100 is providedwith a temperature detecting section 7. The temperature detectingsection 7 detects a temperature in the vicinity of the pressuredetecting elements 6 a and 7 a, and inputs the thus detected temperatureinformation to the control unit 12.

The rotation drive section 10 is an actuator for driving the biaxialrotation mechanism 5 a of the pulse wave detection unit 100. Therotation drive section 10 drives the biaxial rotation mechanism 5 a inaccordance with an instruction issued by the control unit 12, so as torotate the sensor section 6 about the first axis X or rotate the sensorsection 6 about the second axis Y

The air bag drive section 11 includes a pump or the like, and controlsthe amount of air injected into the air bag 2 (the internal pressure ofthe air bag 2) in accordance with an instruction issued by the controlunit 12.

The display section 13 is used for displaying various informationincluding vital information, and includes, for example, a liquid crystaldisplay or the like.

The operation section 14 is an interface for inputting an instructionsignal to the control unit 12, and includes a button and the like forinstructing start of various operations including measurement of vitalinformation.

The memory 15 is a storage medium for storing a pressure signal detectedby the sensor section 6 to be used for calculation of vital informationand various information including the thus calculated vital information,and includes, for example, a flash memory or the like. The memory 15 maybe a removable one.

The control unit 12 mainly includes a processor, and includes a ROM(read only memory) storing programs or the like to be executed by theprocessor, a RAM (random access memory) used as a work memory, and thelike.

The programs include a control program. The ROM is a non-transitorystorage medium from which a computer can read a program. The programstored in the ROM may be one downloaded from another equipment through anetwork to be stored therein.

The control unit 12 has the following functions through execution, bythe processor, of the programs including the control program:

The control unit 12 controls the air bag drive section 11 for adjustingthe amount of air held in the air bag 2, and thus, controls the pressingforce applied by the sensor section 6 to the wrist. The control unit 12thus functions as a pressing force control section.

The control unit 12 controls the rotation drive section 10 to rotate thesensor section 6, and thus, controls the pitch angle and the roll angleof the sensor section 6. The control unit 12 thus functions as arotation control section.

The control unit 12 sets, on the basis of a temperature detected by thetemperature detecting section 7, a reference level of a pressure signal(an output signal) detected by each of the pressure detecting elements 6a and 7 a. Owing to the setting of the reference level, the level of thepressure signal detected by each of the pressure detecting elements 6 aand 7 a can be processed as a value based on the set reference level.The control unit 12 thus functions as a reference level setting section.

The control unit 12 controls the pitch angle of the sensor section 6 toa first value, controls the roll angle of the sensor section 6 to asecond value, and stores, in the memory 15, a pressure signal detectedby a pressure detecting element selected from the sensor section 6 in astate where the sensor section 6 is pressed against the body surface bythe air bag 2 (which state is hereinafter referred to as the pulse wavemeasurement state). The control unit 12 thus functions as a storagecontrol section.

The control unit 12 calculates vital information based on pressuresignals detected in the pulse wave measurement state and stored in thememory 15, and stores the calculated vital information in the memory 15.The control unit 12 thus functions as a vital information calculatingsection.

The vital information may be any information as long as it can becalculated based on a pulse wave. The control unit 12 calculates, as thevital information, for example, blood pressure information such as anSBP (systolic blood pressure) and a DBP (diastolic blood pressure),pulse information such as a pulse count, or heart rate information suchas a heart rate.

Incidentally, the vital information calculating section may be includedanother electronic equipment different from the vital informationmeasuring device. In this case, the pressure signals stored in thememory 15 of the vital information measuring device are transmitted tothe electronic equipment, and vital information is calculated and storedin the electronic equipment.

The control unit 12 determines the second value among a plurality ofsettable roll angles based on the pressure signals detected by thepressure detecting elements of the sensor section 6 in the state wherethe sensor section 6 is pressed against the body surface by the air bag2, and controls the roll angle to the determined second value.

Then, the control unit 12 determines the first value among a pluralityof settable pitch angles based on the pressure signals detected by oneor plural pressure detecting elements of the sensor section 6 with theroll angle controlled to the second value. The control unit 12 thusfunctions as a rotation angle determining section.

The pulse wave detection unit 100, the rotation drive section 10, theair bag drive section 11 and functional blocks of the control unit 12(the pressing force control section, the rotation control section, thereference level setting section, the storage control section and therotation angle determining section) together construct a pulse wavedetecting device.

Now, an operation of the vital information measuring device of thepresent embodiment will be described. The vital information measuringdevice of the present embodiment has a continuous blood pressuremeasurement mode in which the SBP and the DBP are calculated every heartrate to be displayed in the display section 13.

FIG. 6 is a flowchart used for explaining an operation in the continuousblood measurement mode of the vital information measuring device of thepresent embodiment.

Incidentally, in an initial state before a blood pressure measurementinstruction is issued, it is assumed that the pitch angle and the rollangle are both set to, for example, 0 (zero) degree, and the pressingsurface 6 b is vertical to the pressing direction in the pulse wavedetection unit 100.

Here, the state where the pitch angle and the roll angle arerespectively set to 0 (zero) degree is defined as the initial state,which does not limit the present invention. For example, a state wherethe rotation drive section 10 roll-rotates or pitch-rotates the sensorsection 6 so that, with the pulse wave detection unit 100 worn on thewrist, the pressing surface 6 b can be placed in uniform contact withthe skin in accordance with the shape of the wrist may be defined as theinitial state.

When a blood pressure measurement instruction is issued, the controlunit 12 obtains the temperature information detected by the temperaturedetecting section 7, and sets, based on the temperature information, thereference level of the pressure signal detected by each of the pressuredetecting elements 6 a and 7 a of the sensor section 6 (step S1).

In the present embodiment, as each of the pressure detecting elements 6a and 7 a included in the sensor section 6, an element in which apressure signal (an offset level) detected with the pressing surface 6 bin contact with nothing is varied depending on the temperature is used.

Therefore, based on the temperature detected by the temperaturedetecting section 7, the control unit 12 sets the reference level of thepressure signals detected by the pressure detecting elements 6 a and 7a. Owing to the setting of the reference level, the levels of thepressure signals detected by the pressure detecting elements 6 a and 7 aare processed as values based on the set reference level.

Each of the pressure signals detected by the pressure detecting elements6 a and 7 a includes a DC component independent of the heart rate and anAC component varied in accordance with the heart rate. A level of arising point in a waveform of the pressure signal varied in accordancewith the heart rate corresponds to the level of the DC component (the DClevel). A difference between the rising point in the waveform of thepressure signal varied in accordance with the heart rate and a peakcorresponds to the level of the AC component (the AC level).

After step S1, the control unit 12 controls the air bag drive section 11to start injecting air into the air bag 2, so as to increase thepressing force applied by the sensor section 6 to the body surface (stepS2).

The control unit 12 selects either the element row 60 or the element row70 based on the pressure signal detected by each of the pressuredetecting elements of the element row 60 and the element row 70 duringthe increase of the pressing force started in step S2 (step S3).

Here, the control unit 12 selects, from the element row 60 and theelement row 70, one that has been able to more rapidly occlude theradial artery T during the increase. Now, the processing performed instep S3 will be described in detail with reference to FIG. 7.

FIG. 7 is a flowchart used for explaining details of step S3 of FIG. 6.

During the increase of the pressing force started in step S2, thecontrol unit 12 determines, based on the pressure signal detected byeach of the pressure detecting elements 6 a of the element row 60, atarget element (hereinafter referred to as the first target element)corresponding to one pressure detecting element positioned above theradial artery T out of all the pressure detecting elements 6 a includedin the element row 60 (step S30).

For example, the control unit 12 divides the pressure signal detected byeach pressure detecting element 6 a into the AC component and the DCcomponent at arbitrary timing, and determines, as the first targetelement, a pressure detecting element 6 a having an AC level equal to ormore than an AC threshold value and having a DC level equal to or lessthan a DC threshold value.

Besides, when there are a plurality of pressure detecting elements 6 ahaving an AC level equal to or more than the AC threshold value andhaving a DC level equal to or less than the DC threshold value, thecontrol unit 12 determines, as the first target element, one having themaximum AC level and the minimum DC level out of the plural pressuredetecting elements 6 a.

The control unit 12 stores, in the RAM, an ID of the element row 60, anID of the first target element determined in step S30, a pressure signaldetected by the first target element, detection time of the pressuresignal, and a pressing force applied by the air bag 2 at the detectiontime in association with one another (step S31).

After step S31, the control unit 12 determines, based on the pressuresignal of the first target element at each detection time stored in theRAM, whether or not the AC level of the pressure signal detected by thefirst target element determined in step S30 has passed a peak (stepS32).

Specifically, the control unit 12 compares a first AC level of apressure signal corresponding to detection time immediately before thedetection time of the pressure signal of the first target elementdetermined in step S30 with a second AC level of the pressure signal ofthe first target element determined in step S30.

Then, when the second AC level is lower than the first AC level by avalue equal to or more than a threshold value, the control unit 12determines that the AC level of the pressure signal detected by thefirst target element determined in step S30 has passed the peak.

When the second AC level is not lower than the first AC level by thevalue equal to or more than the threshold value, or when merely one AClevel of the pressure signal of the first target element is stored inthe RAM, the control unit 12 determines that the AC level of thepressure signal detected by the first target element determined in stepS30 has not passed the peak.

When it is determined as NO in step S32, the control unit 12 returns theprocessing to step S30.

When it is determined as YES in step S32, the control unit 12 determineswhether or not the AC level of the pressure signal detected by the firsttarget element determined in step S30 has reached an occlusioncompletion determination threshold value (hereinafter referred to as thefirst occlusion completion determination threshold value) smaller thanthe maximum value of the AC level of the pressure signal of the firsttarget element stored in the RAM (step S33).

The first occlusion completion determination threshold value is set to avalue obtained by multiplying the maximum value of the AC level of thepressure signal of the first target element stored in the RAM by acoefficient α that is larger than 0 and smaller than 1.

The first occlusion completion determination threshold value is a valueused for determining whether or not the radial artery T has beenoccluded by the element row 60.

The coefficient α is set to a value sufficient for assuringdetermination accuracy for this purpose. The coefficient α is set to,for example, 0.5.

When it is determined as NO in step S33, the control unit 12 returns theprocessing to step S30.

When it is determined as YES in step S33, the control unit 12 performsprocessing of step S38.

Concurrently with the processing of step S30 to step S33, the controlunit 12 performs processing of step S34 to step S37.

In step S34, the control unit 12 determines a target element(hereinafter referred to as the second target element) corresponding toone pressure detecting element positioned above the radial artery T fromall the pressure detecting elements 7 a included in the element row 70based on the pressure signal detected by each of the pressure detectingelements 7 a of the element row 70 during the increase of the pressingforce started in step S2.

A method for determining the second target element is the same as themethod for determining the first target element. It is noted that theprocessing of step S34 is performed at the same time as the processingof step S30.

In step S35 following step S34, the control unit 12 stores, in the RAM,an ID of the element row 70, an ID of the second target elementdetermined in step S34, a pressure signal detected by the second targetelement, detection time of the pressure signal and a pressing forceapplied by the air bag 2 at the detection time in association with oneanother.

In step S36 following step S35, the control unit 12 determines, based onthe pressure signal of the second target element at each detection timestored in the RAM, whether or not the AC level of the pressure signaldetected by the second target element determined in step S34 has passeda peak. A method for this determination is the same as that of step S32.

When it is determined as NO in step S36, the control unit 12 returns theprocessing to step S34.

When it is determined as YES in step S36, the control unit 12 determineswhether or not the AC level of the pressure signal detected by thesecond target element determined in step S34 has reached an occlusioncompletion determination threshold value (hereinafter referred to as thesecond occlusion completion determination threshold value) smaller thanthe maximum value of the AC level of the pressure signal of the secondtarget element stored in the RAM (step S37).

The second occlusion completion determination threshold value is set toa value obtained by multiplying the maximum value of the AC level of thepressure signal of the second target element stored in the RAM by thecoefficient α.

When it is determined as NO in step S37, the control unit 12 returns theprocessing to step S34. When it is determined as YES in step S37, thecontrol unit 12 performs processing of step S38.

In step S38, the control unit 12 selects, from the element row 60 andthe element row 70, an element row including a target element whose AClevel has reached the occlusion completion determination threshold valuepriorly.

In other words, when the detection time of the pressure signal of thefirst target element at which the AC level has reached the firstocclusion completion determination threshold value is earlier than thedetection time of the pressure signal of the second target element atwhich the AC level has reached the second occlusion completiondetermination threshold value, namely, when timing of determination ofYES in step S33 is earlier than timing of determination of YES in stepS37, the element row 60 is selected in step S38.

On the contrary, when the detection time of the pressure signal of thefirst target element at which the AC level has reached the firstocclusion completion determination threshold value is later than thedetection time of the pressure signal of the second target element atwhich the AC level has reached the second occlusion completiondetermination threshold value, namely, when the timing of determinationof YES in step S37 is earlier than the timing of determination of YES instep S33, the element row 70 is selected in step S38.

The control unit 12 halts the processing of step S30 to step S37 whenthe element row is selected in step S38. The element row selected instep S38 will be hereinafter referred to as the selected element row.

Next, the control unit 12 sets, as a first pressing value, a pressingforce (HDP_(max)) of the air bag 2 applied at the time when the AC levelof the target element determined in the above-described selected elementrow stored in the RAM has reached the occlusion completion determinationthreshold value (step S39). Among the target elements determined in theselected element row, a target element whose AC level has reached theocclusion completion determination threshold value is sometimes referredto as the target element at the time of the occlusion completion.

Next, the control unit 12 sets, as a second pressing value, a pressingforce (HDP_(ACmax)) of the air bag 2 applied at the time when the AClevel of the target element determined in the above-described selectedelement row stored in the RAM has reached the maximum value (step S40).

Here, one of the element row 60 and the element row 70 is selected asthe selected element row based on the pressure signals detected by thepressure detecting elements 6 a and 7 a, but it may be preliminarilydetermined which of the element row 60 and the element row 70 includedin the sensor section 6 is to be selected as the selected row element.

For example, when the element row 60 is preliminarily set as theselected element row, the processing of step S34 to step S37 and theprocessing of step S38 can be omitted. In this case, when it isdetermined as YES in step S33, processing of step S39 and following stepis performed.

FIG. 8 is a diagram illustrating change in the pressure signal detectedby the target element determined in the selected element row selected instep S38 of FIG. 7. The abscissa indicates time and the ordinateindicates a pressure value. A pressure value at each time corresponds tothe level of the pressure signal detected by the target elementdetermined at that time.

When a blood pressure measurement instruction is issued, the referencelevel of the sensor section 6 is set before time t0 (step S1 of FIG. 6).Then, the pressing force increase is started at time t0 (step S2 of FIG.6).

When the pressing force is started to increase, the AC level of thepressure signal detected by the target element reaches a peak (AC_(max))at time t1, and reaches a value obtained by multiplying the AC_(max) bythe coefficient α (that is, 0.5 here) at time t2. Then, the selectedelement row is determined at time t2.

Incidentally, in a period between time t0 and time t2, the targetelement positioned above the radial artery T is determined at each timein each of the element rows 60 and 70.

At time t2, the pressing force (HDP_(max)) applied at time t2 is set asthe first pressing value (step S39 of FIG. 7). Besides, at time t2, thepressing force (HDP_(ACmax)) applied at time t1 is set as the secondpressing value (step S40 of FIG. 7).

Referring to FIG. 6 again, when the selected element row is determinedby the processing of step S3, the control unit 12 controls the pressingforce applied by the air bag 2 to the first pressing value set in stepS39 of FIG. 7, and holds the pressing force in this state (step S4).

In the state where the pressing force is held at the first pressingvalue, the control unit 12 obtains the DC levels detected by the pluralpressure detecting elements included in the selected element row, and onthe basis of the thus obtained DC levels, determines a roll angle(hereinafter referred to as the optimal roll angle) to be employed forcontrol at the time of generating correction data in step S14 andfollowing steps, and at the time of continuous blood pressuremeasurement (step S5).

FIG. 9 is a flowchart used for explaining details of step S5 of FIG. 6.

First, the control unit 12 controls the rotation drive section 10 tocontrol the roll angle to an arbitrary value (step S51).

Next, the control unit 12 obtains the DC levels of pressure signalsrespectively detected by a first pressure detecting element (a targetelement determined at time t2 of FIG. 8) corresponding to the targetelement at the time of the occlusion completion among the pressuredetecting elements of the selected element row, a second pressuredetecting element adjacent on the radius side to the first pressuredetecting element, and a third pressure detecting element adjacent onthe ulna side to the first pressure detecting element (step S52).

Next, the control unit 12 calculates flatness of a graph correspondingto the relationship among the obtained three DC levels and the positionsof the first to the third pressure detecting elements, and stores, inthe RAM, the calculated flatness in association with the value of theroll angle currently employed by control (step S53).

For example, the control unit 12 obtains dispersion or standarddeviation of the three DC levels, and regards the reciprocal of theobtained dispersion or standard deviation as the flatness. The flatnessis defined as a numerical value corresponding to smallness of variationof these three DC levels.

Next, the control unit 12 determines whether or not the flatness hasbeen calculated with respect to each of all the controllable roll angles(step S54).

When the flatness has not been calculated with respect to all thecontrollable roll angles (step S54: NO), the control unit 12 controlsthe rotation drive section 10 to make a change to a roll angle for whichthe flatness has not been calculated (step S55), and thereafter, theprocessing of step S52 and following steps is performed.

When the flatness has been calculated with respect to all the rollangles (step S54: YES), the control unit 12 determines, as the optimalroll angle, a roll angle in association with the maximum flatness(namely, the minimum variation of the DC levels) among the roll anglesstored in the RAM through the processing of step S53 (step S56).Incidentally, it is preferable that the control unit 12 waits for aprescribed time period after controlling the roll angle to an arbitraryvalue in step S51, and obtains the DC levels of the pressure signalsdetected by the first to third pressure detecting elements of theselected element row at timing after the time period has elapsed.Immediately after changing the roll angle from one value to anothervalue, a pressing posture of the sensor section 6 against the bodysurface is changed, and hence, there is a possibility that the bloodflow is largely varied. Therefore, when the DC levels of the pressuresignals are detected after waiting for a little after the control of theroll angle to an arbitrary value, the influence of such blood flowvariation can be reduced.

FIGS. 10A to 10C are diagrams illustrating states where the roll angleof the pulse wave detection unit 100 of FIG. 1 is controlled to threevalues. FIG. 10A illustrates a state where the roll angle is controlledto +θa degrees. FIG. 10B illustrates a state where the roll angle iscontrolled to 0 (zero) degree. FIG. 10C illustrates a state where theroll angle is controlled to −θa degrees. It is noted that θa is anarbitrary value.

FIG. 11 is a graph illustrating a relationship between a DC level of apressure signal detected by each pressure detecting element of theselected element row with the roll angle controlled as illustrated inFIGS. 10A to 10C and the position of the pressure detecting element.

A curve 110 illustrated in FIG. 11 corresponds to an example of the DClevel of the pressure signal detected by each pressure detecting elementin the state of FIG. 10A. In the state of FIG. 10A, the end of theselected element row on the side of the radius TB is in a position closeto the radius TB. Therefore, the curve 110 has a shape having a higherDC level in the end on the side of the radius TB.

A curve 111 illustrated in FIG. 11 corresponds to an example of the DClevel of the pressure signal detected by each pressure detecting elementin the state of FIG. 10B. In the state of FIG. 10B, a pressure from theradius TB is lower than in the state of FIG. 10A. Therefore, theinclination of the curve 111 is gentle as compared with the inclinationof the curve 110.

A curve 112 illustrated in FIG. 11 corresponds to an example of the DClevel of the pressure signal detected by each pressure detecting elementin the state of FIG. 10C. In the state of FIG. 10C, the pressure fromthe radius TB is lower than in the state of FIG. 10B. Therefore, theinclination of the curve 112 is gentle as compared with the inclinationof the curve 111, and has the highest flatness among the three curves110, 111 and 112.

In this manner, when the DC level of the pressure signal detected byeach pressure detecting element of the element row is observed, adistribution of the pressure from a hard tissue such as a bone or atendon can be grasped.

Incidentally, the pressing force employed in determining the optimalroll angle preferably has a value that is not too large to cause achange in the curve such as the curves 110 to 112 by changing the rollangle. Besides, the pressing force employed in determining the optimalroll angle preferably has a value that is sufficiently large fordetecting a pressure signal from a hard tissue (for sufficientlyoccluding the radial artery T).

In other words, when the coefficient α is set to an appropriate value,the pressing force employed in determining the optimal roll angle can beset to an appropriate magnitude, and hence, a distribution of thepressure from a hard tissue can be accurately grasped.

Each curve illustrated in FIG. 11 is formed by using DC levels ofpressure signals detected by all the pressure detecting elementsincluded in the selected element row. Below the selected element row,the radius, the radial artery and the tendon are present in this order.

Therefore, the shape of each curve illustrated in FIG. 11 can be mainlyany of the following three patterns: A shape in which a pressure fromthe radius is strongly detected, and a DC level of a pressure detectingelement, which is positioned closest to the radius (in the radius-sideend) out of the pressure detecting elements included in the selectedelement row, is higher than a DC level of a pressure detecting element,which is positioned closest to the ulna (in the ulna-side end); a shapein which a pressure from a tendon is strongly detected, and the DC levelof the pressure detecting element in the radius-side end is lower thanthe DC level of the pressure detecting element in the ulna-side end; anda flat shape.

Accordingly, in step S53 of FIG. 9, the control unit 12 may calculatethe flatness of each curve illustrated in FIG. 11 with the pressuredetecting element in the radius-side end among the pressure detectingelements included in the selected element row regarded as the secondpressure detecting element, and with the pressure detecting element inthe ulna-side end among the pressure detecting elements included in theselected element row regarded as the third pressure detecting element.

Alternatively, the control unit 12 may obtain, in step S52 of FIG. 9,the DC levels of the pressure signals detected by the two pressuredetecting elements respectively positioned in the radius-side end andthe ulna-side end of the selected element row, and may define, in stepS53 of FIG. 9, a reciprocal of a difference between these two DC levelsas the flatness of the curve illustrated in FIG. 11.

When a graph illustrating the relationship between the positions of theplural pressure detecting elements included in the selected element rowand the DC levels detected by these is flatter, it means that theinfluence of the pressure from a hard tissue is smaller and the radialartery T can be pressed without being disturbed by the hard tissue.

In order to obtain a state where the radial artery T can be pressedwithout being disturbed by a hard tissue, the control unit 12 calculatesthe flatness with respect to each of all the controllable roll angles,and determines, as the optimal roll angle, a roll angle whose flatnessthus calculated has the maximum value.

Incidentally, the control unit 12 may calculate the flatness based onvariation in the DC level of pressure signals detected by all thepressure detecting elements included in the selected element row, so asto determine, as the optimal roll angle, a roll angle whose flatnessthus calculated has the maximum value.

As described above, when the number of DC levels used for thecalculation of the flatness is limited to two or three, computationalcomplexity can be reduced. As a result, reduction of power consumptionand fast determination of the optimal roll angle can be realized.

Besides, the control unit 12 determines the optimal roll angle based onthe DC levels of the pressure signals detected by a plurality ofpressure detecting elements of one element row selected from the elementrow 60 and the element row 70 in step S5 of FIG. 6, which does not limitthe present invention. The control unit 12 may determine the optimalroll angle based on DC levels of pressure signals detected by thepressure detecting elements of each of the element row 60 and theelement row 70.

For example, the control unit 12 obtains DC levels of the pressuresignals detected by the plural pressure detecting elements in each ofthe element row 60 and the element row 70 in step S52 of FIG. 9.

Then, in step S53 of FIG. 9, the control unit 12 calculates the flatnessbased on the plural DC levels obtained with respect to the element row60, stores the result in association with a roll angle currentlyemployed by control, calculates the flatness based on the plural DClevels obtained with respect to the element row 70, and stores theresult in association with the roll angle currently employed by control.

After calculating the flatness of each element row with respect to allthe roll angles, the control unit 12 may determine the roll angle inassociation with the maximum flatness as the optimal roll angle in stepS56 of FIG. 9.

Referring to FIG. 6 again, after step S5, the control unit 12 controlsthe roll angle of the sensor section 6 to the optimal roll angledetermined in step S5 (step S6). Besides, the control unit 12 controlsthe pressing force applied by the air bag 2 to the second pressing valueset in step S40 of FIG. 7, and holds the pressing force in this state(step S7).

The processing of step S5 to step S7 will be described with reference toFIG. 8. Incidentally, FIG. 8 illustrates exemplified operationsperformed when the roll angle can be controlled to the three values of 0(zero) degree, +θ1 degrees and −θ1 degrees. It is noted that θ1 is anarbitrary value.

As illustrated in FIG. 8, the roll angle is controlled to 0 (zero)degree in a period from time t2 to time t3, and the flatness iscalculated in this state. Subsequently, in a period from time t3 to timet4, the roll angle is controlled to +θ1 degrees, and the flatness iscalculated in this state. Subsequently, in a period from time t4 to timet5, the roll angle is controlled to −θ1 degrees, and the flatness iscalculated in this state.

In the exemplified case illustrated in FIG. 8, the flatness calculatedin the state where the roll angle is controlled to 0 (zero) degree isthe maximum (the optimal roll angle=0 (zero) degree). Therefore, thecontrol unit 12 controls the roll angle of the sensor section 6 to 0(zero) degree in a period from time t5 to time t6. Besides, the controlunit 12 holds the pressing force at the second pressing value(HDP_(ACmax)) in the period from time t5 to time t6.

Incidentally, since the roll angle corresponding to the maximum flatnessis 0 (zero) degree in the exemplified case of FIG. 8, the roll angle ischanged from −θ1 degrees to 0 (zero) degree in the period from time t5to time t6. If the flatness is maximum in the period from time t4 totime t5, however, there is no need to change the roll angle in theperiod from time t5 to time t6. In other words, the determination of theoptimal roll angle and the control to the optimal roll angle may besimultaneously performed.

Referring to FIG. 6 again, after step S7, the control unit 12 determinesa pitch angle to be employed by control at the time of the generation ofcorrection data in step S14 and following steps and at the time of thecontinuous blood pressure measurement (hereinafter referred to as theoptimal pitch angle) based on DC levels of the pressure signals detectedby the plural pressure detecting elements included in each of theelement row 60 and the element row 70 (step S8). In the exemplified caseof FIG. 8, the processing of step S8 is performed in a period from timet6 to time t7.

FIG. 12 is a flowchart used for explaining details of step S8 of FIG. 6.

The control unit 12 selects, from the first target elements stored inthe RAM in the process of step S30 to step S37 of FIG. 7, the firsttarget element in association with the pressing force of the secondvalue (HDP_(ACmax)) (step S81).

Besides, the control unit 12 selects, from the second target elementsstored in the RAM in the process of step S30 to step S37 of FIG. 7, thesecond target element in association with the pressing force of thesecond value (HDP_(ACmax)) (step S82).

Incidentally, instead of performing step S81 and step S82, the controlunit 12 may select one first target element positioned above the radialartery T based on the pressure signal detected by each of the pressuredetecting elements 6 a of the element row 60, and may select one secondtarget element positioned above the radial artery T based on thepressure signal detected by each of the pressure detecting elements 7 aof the element row 70.

After selecting the first target element and the second target element,the control unit 12 compares the DC level of the pressure signaldetected by the selected first target element (hereinafter referred toas the peripheral-side DC level) with the DC level of the pressuresignal detected by the selected second target element (hereinafterreferred to as the center-side DC level), and sets the rotationdirection and the rotation amount of the pitch rotation of the sensorsection 6 based on the comparison result and the current pitch angle(step S83).

Specifically, when the peripheral-side DC level is lower than thecenter-side DC level, the control unit 12 sets the rotation direction tothe positive direction (the counterclockwise direction in FIG. 1).Alternatively, when the center-side DC level is lower than theperipheral-side DC level, the control unit 12 sets the rotationdirection to the negative direction (the clockwise direction in FIG. 1).

Besides, the control unit 12 sets the rotation amount to a half value ofa difference between the absolute value of the current pitch angle ofthe sensor section 6 and the maximum value or the minimum value of theabsolute value of the pitch angle that can be employed when the sensorsection 6 is rotated in the rotation direction set in theabove-described method from the current pitch angle.

It is assumed, for example, that the pitch angle is changeable by 5degrees at the most in each of the positive direction and the negativedirection from 0 (zero) degree. When the current pitch angle is 0 (zero)degree and the set rotation direction is the positive direction, therotation amount is set to 2.5 degrees, that is, a half of a differenceof 5 degrees, that is, the maximum value of the absolute value of thechangeable pitch angle in the rotation from the current pitch angle inthe positive direction, and 0 (zero) degree, that is, the current pitchangle.

Alternatively, when the current pitch angle is +2.5 degrees and the setrotation direction is the negative direction, the rotation amount is setto 1.25 degrees, that is, a half of a difference of 0 (zero) degree,that is, the minimum value of the absolute value of the changeable pitchangle in the rotation from the current pitch angle in the negativedirection, and 2.5 degrees, that is, the current pitch angle.

Alternatively, when the current pitch angle is +2.5 degrees and the setrotation direction is the positive direction, the rotation amount is setto 1.25 degrees, that is, a half of a difference of 5 degrees, that is,the maximum value of the absolute value of the changeable pitch angle inthe rotation from the current pitch angle in the positive direction, and2.5 degrees, that is, the current pitch angle.

Then, the control unit 12 pitch-rotates the sensor section 6 in the setrotation direction correspondingly to the set rotation amount (stepS84).

After step S84, the control unit 12 determines whether or not theprocessing of step S84 has been performed a prescribed number of times(step S85). As the prescribed number of times, a value of 2 or more isset. The prescribed number of times is preferably set to 3 inconsideration of reduction of time necessary for the determination ofthe optimal pitch angle and the determination accuracy of the optimalpitch angle.

When it is determined as NO in step S85, the processing of step S83 andstep S84 is performed again. When it is determined as YES in step S85,the control unit 12 determines the current pitch angle as the optimalpitch angle (step S86).

FIG. 13 and FIG. 14 are diagrams illustrating examples of the pressuresignals detected by the first target element and the second targetelement. As illustrated in FIG. 13, when the DC level of the pressuresignal detected by the second target element is lower than the DC levelof the pressure signal detected by the first target element, the pitchrotation is performed in the direction where the element row 70 comescloser to the body surface (in the negative direction). When the pitchrotation is repeated, a state in which the two DC levels are close toeach other as illustrated in FIG. 14 can be obtained.

Through the processing of step S8, the DC levels of the pressure signalsdetected by the first target element positioned above the radial arteryT in the element row 60 and the second target element positioned abovethe radial artery T in the element row 70 become close to each other,and the optimal pitch angle realizing a state where the radial artery Tcan be pressed similarly by the element row 60 and the element row 70can be determined.

Incidentally, the control unit 12 may calculate a first average value ofthe DC levels of the pressure signals detected by the pressure detectingelements 6 a of the element row 60 in step S81, calculate a secondaverage value of the DC levels of the pressure signals detected by thepressure detecting elements 7 a of the element row 70 in step S82, anddetermine the pitch rotation direction in step S83 by using the firstaverage value instead of the peripheral-side DC level and using thesecond average value instead of the center-side DC level. The optimalpitch angle can be also determined in this manner.

Alternatively, the control unit 12 can determine the optimal pitch anglein step S8 as follows.

After performing the processing of step S81 and step S82 illustrated inFIG. 12, the control unit 12 successively controls the pitch angle toall the settable values for calculating a difference between theperipheral-side DC level and the center-side DC level obtained in astate where the pitch angle is controlled to each of the values, andstores, in the RAM, the calculated difference in association with thepitch angle currently employed by control.

Then, the control unit 12 determines, among the pitch angles thus storedin the RAM, a pitch angle having the smallest difference stored inassociation as the optimal pitch angle.

According to this modification, a pitch angle obtained in a state wherethe DC levels of the pressure signals detected by the first targetelement and the second target element are the closest is determined asthe optimal pitch angle.

According to this modification, the control unit 12 may calculate anaverage value of the DC levels of the pressure signals detected by thepressure detecting elements 6 a of the element row 60 in step S81,calculate an average value of the DC levels of the pressure signalsdetected by the pressure detecting elements 7 a of the element row 70 instep S82, and calculate and store a difference of these two averagevalues instead of the difference between the peripheral-side DC leveland the center-side DC level.

Alternatively, the control unit 12 may determine, in step S8, theoptimal pitch angle based on the AC levels of the pressure signalsdetected by the pressure detecting elements included in the element row60 and the element row 70 by a method described in Patent Literature 1.

Referring to FIG. 6 again, after determining the optimal pitch angle instep S8, the control unit 12 controls the pitch angle of the sensorsection 6 to the optimal pitch angle determined in step S8 (step S9).

Incidentally, in the exemplified processing of step S8 illustrated inFIG. 12, the determination of the optimal pitch angle in step S86 andthe processing of step S9 are simultaneously performed.

Next, the control unit 12 reduces the pressing force applied by the airbag 2 to a reset value (a value HDP_(RESET) illustrated in FIG. 8)smaller than the second pressing value held in step S7 and larger than 0(zero), and holds the pressing force at the reset value (step S10).

The control unit 12 obtains, in this state, the temperature informationdetected by the temperature detecting section 7, calculates a differencebetween the obtained temperature information and the temperatureinformation obtained in step S1, and determines whether or not thedifference is equal to or more than a temperature threshold value (stepS11).

When it is determined that the difference is less than the temperaturethreshold value, namely, it is determined that there is no largedifference in the temperature of the sensor section 6 between the timeof the processing of step S1 and the current time (step S11: NO), thecontrol unit 12 performs processing of step S14.

When it is determined that the difference is equal to or more than thetemperature threshold value, namely, it is determined that there is alarge difference in the temperature of the sensor section 6 between thetime of the processing of step S1 and the current time (step S11: YES),the control unit 12 controls the pressing force to 0 (zero) (step S12),and thereafter, re-sets the reference level of the pressure signaldetected by each pressure detecting element of the sensor section 6based on the current temperature information (step S13). After step S13,the processing of step S14 and following steps is started.

In step S14, the control unit 12 increases the pressing force from thecurrent value to a preliminarily determined value sufficient foroccluding the radial artery T (from time t8 to time t9 of FIG. 8).

The control unit 12 controls a rate of increasing the pressing force instep S14 to a lower rate than a rate of increasing the pressing force instep S2, which does not limit the invention.

Incidentally, the processing of step S11 to step S13 of FIG. 6 is notindispensable but can be omitted. In this case, the processing of stepS14 follows step S10.

The control unit 12 stores, in the memory 15, the pressure signalsdetected by the pressure detecting elements of the sensor section 6during the increase of the pressing force started in step S14, and basedon the pressure signals thus stored, determines an optimal pressuredetecting element out of all the pressure detecting elements 6 a and 7a.

The control unit 12 determines, for example, a pressure detectingelement having detected a pressure signal having the maximum AC levelduring the increase of the pressing force as the optimal pressuredetecting element. Besides, the control unit 12 determines, as anoptimal pressing force, a pressing force applied when this pressuresignal is detected (step S15).

After step S15, the control unit 12 generates pulse wave envelope databased on the pressure signals detected by the optimal pressure detectingelement during the increase of the pressing force and stored in thememory 15.

The pulse wave envelope data is data in which the pressing force of thesensor section 6 (the internal pressure of the air bag 2) is inassociation with the AC level of the pressure signal detected by theoptimal pressure detecting element with the optimal pressure detectingelement pressed against the body surface with that pressing force.

Then, the control unit 12 calculates the SBP and the DBP based on thethus generated pulse wave envelope data, and generates the correctiondata to be used in continuous blood pressure measurement of step S18based on the pressure signals detected by the optimal pressure detectingelement during the increase of the pressing force started in step S14and the calculated SBP and DBP, and stores the correction data in thememory 15 (step S16).

Thereafter, the control unit 12 holds the pressing force at the optimalpressing force determined in step S15 (step S17, time t10 of FIG. 8).

Then, the control unit 12 successively stores, in the memory 15, thepressure signals detected by the optimal pressure detecting elementdetermined in step S15, and based on the AC levels of the pressuresignals thus stored and the correction data generated in step S16,calculates the SBP and the DBP every heart rate and stores these in thememory 15 (step S18). The control unit 12 displays the calculated SBPand DBP in, for example, the display section 13 to inform the user.

The control unit 12 repeatedly performs the processing of step S18 untilan instruction to stop the blood pressure measurement is issued, andwhen the stop instruction is issued, the blood pressure measurementprocessing is ended.

As described so far, the vital information measuring device of thepresent embodiment determines the optimal roll angle in step S5, anddetermines the optimal pitch angle in step S8 with the roll angle of thesensor section 6 controlled to the optimal roll angle.

In this manner, through the procedures of determining the optimal rollangle and determining the optimal pitch angle in the state where theroll angle is controlled to the determined optimal roll angle, theoptimal pitch angle can be determined with reducing the influence of thepressure from a hard tissue such as a bone or a tendon on the detectionaccuracy of the pulse wave.

At the time of obtaining a pressure signal necessary for generating thecorrection data and at the time of the continuous blood pressuremeasurement, in order to increase the detection accuracy of the pulsewave, an ideal pressing state where the pressing state of the radialartery T by the element row 60 is substantially equivalent to thepressing state of the radial artery T by the element row 70 ispreferably obtained. The processing of step S8 is processing fordetermining the optimal pitch angle for realizing this ideal pressingstate.

According to the vital information measuring device of the presentembodiment, in the state where the roll angle is controlled to theoptimal roll angle at which a signal level derived from a pressure froma hard tissue such as a bone or a tendon is low, the optimal pitch anglefor realizing the ideal pressing state can be determined.

Therefore, the determination of the optimal pitch angle for obtainingthe ideal pressing state can be performed highly accurately. As aresult, the detection accuracy of the pulse wave detected through theprocessing of step S14 and following steps can be improved to improvethe measurement accuracy of the vital information.

Besides, in the vital information measuring device of the presentembodiment, the pressing force (the second pressing value) applied indetermining the optimal pitch angle in step S8 is set to be smaller thanthe pressing force (the first pressing value) applied in determining theoptimal roll angle in step S5.

When the second pressing value is set to be smaller than the firstpressing value in this manner, the optimal pitch angle can be determinedin a state where the radial artery T is appropriately pressed, and thedetermination accuracy of the optimal pitch angle can be improved.

The state where the radial artery T is appropriately pressed refers to astate where the radial artery T is not occluded and the pressed surfaceof the radial artery T is flat and influence of tone is negligible,namely, what is called a tonometry state.

In the exemplified operation illustrated in FIG. 6, the pressing forceis held, in step S7, at the pressing force (HDP_(ACmax)) with which theAC level of the target element of the selected element row can be themaximum value (AC_(max)). The state where the pressing force is held atHDP_(ACmax) is regarded to be the closest to the tonometry state.Therefore, when the second pressing value is set to HDP_(ACmax), thedetermination accuracy of the optimal pitch angle can be improved.

Incidentally, the second pressing value is set to HDP_(ACmax) in theexemplified operation illustrated in FIG. 6, which does not limit thepresent invention. The second pressing value may be an arbitrary valuecorresponding to a range of the pressing force where change of the DClevel of the target element determined at each time in the selectedelement row is equal to or less than a change threshold value. Apressing force with which the change of the DC level of the targetelement is the smallest is substantially equal to a pressing force withwhich the AC level of the target element is the maximum.

In other words, the second pressing value may be set to a value in thevicinity of the pressing force with which the AC level of the targetelement determined at each time in the selected element row is themaximum.

Specifically, the second pressing value is preferably set to anarbitrary numerical value corresponding to a range of the pressing forcewith which the AC level of the target element determined at each time inthe selected element row is as high as 0.9 times or more of the maximumvalue (AC_(max) illustrated in FIG. 8), and is more preferably set to anarbitrary numerical value corresponding to a range of the pressing forcewith which it is as high as 0.95 times or more of the maximum value.

The state where the pressing force is held at HDP_(ACmax) is regarded tobe the closest to the tonometry state. Therefore, the second pressingvalue is most preferably set to HDP_(ACmax) as in the exemplifiedoperation of FIG. 6.

Besides, according to the vital information measuring device of thepresent embodiment, either one of the element row 60 and the element row70 is selected as the selected element row in step S3. Then, the optimalroll angle is determined based on the pressure signals detected by theplural pressure detecting elements of the one selected element row.

Specifically, the control unit 12 selects an element row that haspriorly occluded the radial artery T as the selected element row in stepS3, and determines the optimal roll angle in the state where thepressing force is held at the pressing force applied when the selectedelement row occluded the radial artery T.

Owing to this configuration, the optimal roll angle can be determinedbased on the pressure signals output from an element row not affected byblood flow change or the like caused by the occlusion of the radialartery T. In other words, the pressure signal output from the selectedelement row can be improved in the reliability, and the determinationaccuracy of the optimal roll angle can be improved.

Besides, since the element row that has been able to occlude the radialartery T in a shorter period of time is selected as the selected elementrow, time necessary for the determination of the optimal roll angle canbe reduced to reduce time required for starting the blood pressuremeasurement.

Furthermore, in the vital information measuring device of the presentembodiment, the optimal roll angle is determined based on the DC levelsof the pressure signals detected by the pressure detecting elements ofeither one of the element rows 60 and 70. Since the optimal roll angleis thus determined based on the DC levels of the pressure signals, theroll angle minimally affected by a pressure from a hard tissue such as abone or a tendon can be highly accurately determined.

Incidentally, the control unit 12 may determine, in step S5, the optimalroll angle based on the absolute values of the pressure signals detectedby the pressure detecting elements of the selected element row insteadof the DC levels of the pressure signals detected by the pressuredetecting elements of the selected element row.

The state where the pressing force is held at the first pressing valuein step S4 is a state where the radial artery T is occluded by theselected element row. In other words, in this state, the AC levels ofthe pressure signals detected by the pressure detecting elements of theselected element row are sufficiently low.

Therefore, even when the optimal roll angle is determined based on theabsolute values of the pressure signals detected by the plural pressuredetecting elements of the selected element row, the influence of thepressure from a hard tissue such as a bone or a tendon can be reducedwith given accuracy. When the DC levels are used as described above, adistribution of the pressure from a hard tissue such as a bone or atendon can be more accurately detected, and hence the determinationaccuracy of the optimal roll angle can be improved.

Besides, in the vital information measuring device of the presentembodiment, the optimal pitch angle is determined based on the DC levelsof the pressure signals detected by the plural pressure detectingelements included in each of the element rows 60 and 70. Since theoptimal pitch angle is thus determined based on the DC levels of thepressure signals, the optimal pitch angle with which the ideal pressingstate can be realized can be highly accurately determined. The reason isas follows.

In the vital information measuring device of the present embodiment, theelement row 60 and the element row 70 press different portions of aliving body. Besides, when the radial artery T is started to be occludedon the peripheral side having high resistance prior to the center side,a reflected wave is caused accordingly. The reflected wave issuperimposed on a pressure signal detected by a pressure detectingelement of the element row 70 positioned above the radial artery T.

In this manner, due to a difference in the composition of a subcutaneoustissue of the pressed portion of the living body, and the occurrence ofa reflected wave and the like, even in the ideal pressing state, the AClevel of a pressure signal detected by a pressure detecting element ofthe element 60 positioned above the radial artery T may be differentfrom the AC level of a pressure signal detected by a pressure detectingelement of the element row 70 positioned above the radial artery T insome cases.

On the other hand, the DC level of the pressure signal detected by thepressure detecting element of the element row 60 positioned above theradial artery T and the DC level of the pressure signal detected by thepressure detecting element of the element row 70 positioned above theradial artery T are not affected by the difference in the composition ofthe subcutaneous tissue of the pressed portion of the living body, andthe occurrence of a reflected wave and the like.

Therefore, when the optimal pitch angle is determined based on the DClevels of the pressure signals detected by the plural pressure detectingelements included in each of the element rows 60 and 70, the optimalpitch angle can be highly accurately determined.

Incidentally, also when the optimal pitch angle is determined based onthe AC levels of the pressure signals detected by the plural pressuredetecting elements included in each of the element rows 60 and 70, theoptimal pitch angle can be determined with given accuracy.

Furthermore, in the vital information measuring device of the presentembodiment, the optimal pitch angle can be determined based on pressuresignals respectively detected by two pressure detecting elements, thatis, one pressure detecting element selected from the element row 60 andone pressure detecting element selected from the element row 70.

When the optimal pitch angle is thus determined based on the pressuresignals of the two pressure detecting elements, the computationalcomplexity necessary for determining the optimal pitch angle can bereduced, so as to reduce the power consumption and reduce the timerequired for starting the blood pressure measurement.

Incidentally, in the exemplified processing of FIG. 12, one element isselected, in step S81 and step S82, from the target elements determinedthrough the processing of step S30 to step S37 of FIG. 7. When one to beused for determining the optimal pitch angle is thus selected from thetarget elements preliminarily determined, the computational complexitynecessary for determining the optimal pitch angle can be reduced. As aresult, the power consumption can be reduced, and the time required forstarting the blood pressure measurement can be reduced.

Besides, in the vital information measuring device of the presentembodiment, after determining the optimal pitch angle, the pressingforce is reduced to the reset value smaller than the second pressingvalue and larger than 0 (zero), and thereafter, the processing of stepS14 and following steps is performed. When the processing of step S14and following steps is thus performed without reducing the pressingforce to 0 (zero), the time required for starting the blood pressuremeasurement can be reduced.

Furthermore, when the processing of step S14 and following steps isperformed with the pressing force once reduced, the optimal pressingforce and the optimal pressure detecting element can be determined withthe sensor section 6 controlled to the optimal roll angle and theoptimal pitch angle, and hence the detection accuracy of the pulse wavecan be improved.

Besides, the vital information measuring device of the presentembodiment re-sets, after determining the optimal pitch angle, thereference level of each pressure detecting element of the sensor section6 with the pressing force reduced to 0 (zero) when there has arisen alarge difference between the temperature information obtained at theinitial state and the current temperature information. When thereference revel is thus re-set, the detection accuracy of the pulse wavein the processing of step S14 and following steps can be improved.

Furthermore, in the vital information measuring device of the presentembodiment, the rate of increasing the pressing force in step S2 ishigher than the rate of increasing the pressing force in step S14.

Owing to this structure, the increase of the pressing force necessaryfor determining the optimal roll angle and the optimal pitch angle canbe rapidly performed, and the time required for starting the bloodpressure measurement can be reduced. On the other hand, since the rateof increasing the pressing force necessary for generating the correctiondata is relatively low, the correction data can be highly accuratelyobtained.

In the vital information measuring device of the present embodiment,before determining the optimal roll angle in step S5, the control unit12 may pitch-rotates the sensor section 6 so as to obtain a gooddetection state of a pressure signal of each of the element row 60 andthe element row 70.

For example, after starting the increase of the pressing force in stepS2, the control unit 12 compares, at regular timing until the processingof step S38 of FIG. 7 is performed, the AC level of the pressure signalof the latest first target element stored in the RAM with the AC levelof the pressure signal of the latest second target element, anddetermines, based on a result of the comparison, whether or not thepitch rotation is necessary.

When a difference between the two AC levels is equal to or more than athreshold value, the control unit 12 determines that the radial artery Tis not satisfactorily flattened by the element row including a targetelement having a relatively lower AC level, and determines that thepitch rotation is necessary. Then, the sensor section 6 is pitch-rotatedin a direction in which this element row of interest comes closer to thebody surface. The rotation amount at this point is arbitrary, and may beset to, for example, a controllable minimum value.

When the difference between the two AC levels is less than the thresholdvalue, the control unit 12 determines that the two element rowsrespectively satisfactorily flatten the radial artery T, and determinesthat there is no need of the pitch rotation.

For example, when the AC level of the latest first target element ishigher than the AC level of the latest second target element by thethreshold value or more at the above-described timing, the control unit12 pitch-rotates the sensor section 6 in the negative direction.

Thus, the AC level of the second target element can be increased. As aresult, as compared with a case where the pitch rotation is notperformed, a possibility of the element row 70 selected as the selectedelement row can be increased, and hence, choices of the element rowsusable for the determination of the optimal pitch angle can beincreased.

FIG. 15 is a flowchart illustrating a modification of the detailedprocessing of step S5 of FIG. 6.

First, the control unit 12 controls the rotation drive section 10 tocontrol the roll angle to an arbitrary angle (step S91).

Next, the control unit 12 obtains the DC levels of pressure signalsrespectively detected by the first pressure detecting element to thethird pressure detecting element among the respective pressure detectingelements of the selected element row, calculates the flatness in thesame manner as in the processing of step S53 based on the three DClevels thus obtained, and stores the flatness in the RAM in associationwith the roll angle currently employed by control (step S92).

Next, the control unit 12 determines whether or not a difference betweenthe DC level of the pressure signal detected by the second pressuredetecting element (hereinafter referred to as the radius-side DC level)and the DC level of the pressure signal detected by the third pressuredetecting element (hereinafter referred to as the ulna-side DC level) isequal to or more than a threshold value (step S93).

When the difference between the radius-side DC level and the ulna-sideDC level is less than the threshold value (step S93: NO), the controlunit 12 controls the rotation drive section 10 to roll-rotate the sensorsection 6 by a minimum angle in the positive direction or the negativedirection (step S94), and thereafter, returns the processing to stepS92.

When the difference between the radius-side DC level and the ulna-sideDC level is equal to or more than the threshold value (step S93: YES),the control unit 12 determines whether or not the radius-aide DC levelis higher than the ulna-side DC level (step S95).

When the radius-side DC level is lower than the ulna-side DC level (stepS95: NO), the control unit 12 restricts the direction of the rollrotation to the positive direction (the counterclockwise direction takenfrom the side of the left elbow) (step S96). In other words, the controlunit 12 excludes, from candidates of the optimal roll angle, roll anglestoward the negative direction from the current roll angle out of rollangles excluding roll angles having been calculated for the flatness.

When the radius-side DC level is higher than the ulna-side DC level(step S95: YES), the control unit 12 restricts the direction of the rollrotation to the negative direction (the clockwise direction taken fromthe side of the left elbow) (step S97). In other words, the control unit12 excludes, from the candidates of the optimal roll angle, roll anglestoward the positive direction from the current roll angle out of theroll angles excluding the roll angles having been calculated for theflatness.

After step S96 and step S97, the control unit 12 determines whether ornot the flatness has been calculated for all angles in the rotationdirection restricted based on the current roll angle as described aboveout of all the settable roll angles (step S98).

When it is determined as NO in step S98, the control unit 12 controlsthe rotation drive section 10 to control the sensor section 6 to a rollangle not calculated for the flatness yet among the settable roll anglesin the restricted rotation direction (step S99).

Then, the control unit 12 obtains the DC levels of the pressure signalsrespectively detected by the first pressure detecting element to thethird pressure detecting element, calculates the flatness in the samemanner as in the processing of step S52 based on the obtained three DClevels, and stores the flatness in the RAM in association with the rollangle currently employed by control (step S100). After step S100, theprocessing returns to step S98.

When it is determined as YES in step S98, the control unit 12determines, as the optimal roll angle, a roll angle in association withthe largest flatness out of the roll angles stored in the RAM throughthe processing of step S92 and step S100 (step S101).

In this manner, according to the modification illustrated in FIG. 15, ascompared with the exemplified processing illustrated in FIG. 9, thenumber of roll angles to be calculated for the flatness can be reduced.Therefore, the computation complexity for determining the optimal rollangle can be reduced, and the power consumption caused in the rollrotation can be reduced.

Incidentally, it is assumed here that the angles settable as the rollangle are three angles of 0 (zero) degree, +θ1 degrees and −θ1 degrees(wherein θ1 is an arbitrary value), and that the arbitrary value used instep S91 is 0 (zero) degree.

In this case, when the processing of the initial step S93 is determinedas YES and step S95 is determined as NO, the control unit 12 determines+θ1 degrees as the optimal roll angle. Alternatively, when theprocessing of the initial step S93 is determined as YES and step S95 isdetermined as YES, the control unit 12 determines −θ1 degrees as theoptimal roll angle.

In this manner, according to this modification, the optimal roll anglecan be also determined without performing the roll rotation.

Although the rotation section 5 is configured to be rotatable about eachof the first axis X and the second axis Y in the vital informationmeasuring device of the present embodiment, the rotation section 5 maybe configured to be rotatable about either one of the first axis X andthe second axis Y.

When the rotation section 5 is configured to be rotatable about merelythe first axis X (configured to be capable of the pitch rotation alone),the control unit 12 may omit the processing of step S5 and step S6 inthe flowchart of FIG. 6 so as to perform the processing of step S7 andfollowing steps after the processing of step S4.

Besides, when the rotation section 5 is configured to be rotatable aboutmerely the first axis X, each of the element row 60 and the element row70 of the sensor section 6 need not include a plurality of pressuredetecting elements, and may be configured to include at least onepressure detecting element. In other words, the sensor section 6 may beconfigured to include at least one pair of pressure detecting elementsof the pressure detecting element 6 a and the pressure detecting element7 a arranged in the direction A. In addition, in a case that three ormore element rows are arranged in the direction A, the pair consists ofthe pressure detecting element included in one of the two element rowsamong the three or more element rows and the pressure detecting elementincluded in the other of the two element rows.

In this configuration, the first target element described with referenceto FIG. 7 is always the same pressure detecting element 6 a, and thesecond target element is always the same pressure detecting element 7 a.Besides, in step S38, the pressure detecting element whose AC level hasreached in advance the occlusion completion determination thresholdvalue is selected.

Besides, in step S39, a pressing force applied at the time when the AClevel of the selected pressure detecting element has reached theocclusion completion determination threshold value is set as the firstpressing value. Furthermore, in step S40, a pressing force applied atthe time when the AC level of the selected pressure detecting elementhas reached a peak is set as the second pressing value.

Furthermore, in step S8, the control unit 12 omits step S81 and step S82of FIG. 12, and in step S83, compares the DC levels of the pressuresignals respectively detected by the pressure detecting element 6 a andthe pressure detecting element 7 a to set the rotation direction and therotation amount of the pitch rotation of the sensor section 6 based onthe result of the comparison and the current pitch angle.

When the rotation section 5 is configured to be rotatable about merelythe second axis Y (configured to be capable of the roll rotation alone),the control unit 12 may omit the processing of step S7 to step S9 in theflowchart of FIG. 6 so as to perform the processing of step S10 andfollowing steps after the processing of step S6.

Besides, when the rotation section 5 is configured to be rotatable aboutmerely the second axis Y, either one of the element row 60 and theelement row 70 may be omitted in the sensor section 6.

For example, when the sensor section 6 is configured to include theelement row 60 alone, step S34 to step S38 are omitted in FIG. 7, andwhen it is determined as YES in step S33, the processing of step S39 andfollowing steps is performed in the operation. Besides, the selectedelement row used in step S39 and following steps is the element row 60.

It should be understood that the present embodiment herein disclosed ismerely illustrative and not restrictive. The scope of the presentinvention is not limited to the above description but is defined byappended claims, and it is intended that equivalents to the appendedclaims and all changes made within the scope thereof are embraced.

For example, the wrist-worn vital information measuring device fordetecting a pulse wave from the radial artery of a wrist has beendescribed so far, but the present invention may be applied to a devicefor detecting a pulse wave from the carotid artery or the dorsalis pedisartery.

Besides, the sensor section 6 may be configured to include three or moreelement rows arranged in the direction A.

In the case of employing this configuration, the control unit 12selects, in step S3 of FIG. 6, an element row having occluded the radialartery T most early among the three or more element rows as the selectedelement row. Alternatively, the control unit 12 preliminarily selectsany one of the three or more element rows as the selected element row.

Besides, in step S8 of FIG. 6, the control unit 12 determines theoptimal pitch angle with which the DC levels or the AC levels ofpressure signals detected by one pressure detecting element selectedfrom each of the three or more element rows are close to one another.

As described so far, the followings are herein disclosed:

A pulse wave detecting device herein disclosed includes: a sensorsection that includes at least one pair of pressure detecting elementsarranged in a direction perpendicular to a first direction; a pressingsection that presses the sensor section against a body surface of aliving body in a state where the first direction crosses a direction ofan artery extending below the body surface; a rotation drive sectionthat rotates the sensor section about an axis extending in the firstdirection; a storage control section that stores, in a storage medium,pressure signals detected by the pressure detecting elements in a statewhere a rotation angle of the sensor section about the axis iscontrolled to a specific value and the sensor section is pressed againstthe body surface by the pressing section; and a rotation angledetermining section that determines the specific value based on DCcomponents of pressure signals detected, in a state where the sensorsection is pressed against the body surface by the pressing section,respectively by a first pressure detecting element and a second pressuredetecting element out of the pressure detecting elements included in thesensor section, the first pressure detecting element and the secondpressure detecting element being different from each other in a positionin the direction perpendicular to the first direction.

In the pulse wave detecting device herein disclosed, the rotation angledetermining section determines, as the specific value, a value of therotation angle with which a difference between the DC component of thepressure signal detected by the first pressure detecting element and theDC component of the pressure signal detected by the second pressuredetecting element is the minimum.

In the pulse wave detecting device herein disclosed, the sensor sectionincludes two element rows each including a plurality of pressuredetecting elements arranged in the first direction, the two element rowsbeing arranged in the direction perpendicular to the first direction,pressure detecting elements disposed in the same position in the firstdirection respectively in the two element rows together form the pair,and the rotation angle determining section selects, as the firstpressure detecting element, one of the plurality of pressure detectingelements included in a first element row out of the two element rowsbased on a group of pressure signals detected by the pressure detectingelements of the first element row, and selects, as the second pressuredetecting element, one of the plurality of pressure detecting elementsincluded in a second element row out of the two element rows based on agroup of pressure signals detected by the pressure detecting elements ofthe second element row.

In the pulse wave detecting device herein disclosed, the rotation angledetermining section performs processing for successively determining, asa target element, one element positioned on the artery from the pressuredetecting elements included in the element rows based on a group ofpressure signals detected by the respective pressure detecting elementsof the element rows during increase of a pressing force applied to thesensor section against the body surface by the pressing section, anddetermines the specific value in a state where the sensor section ispressed against the body surface with a specific pressing force withwhich variation of a DC component of a pressure signal detected by thetarget element successively determined in one element row out of the twoelement rows is equal to or lower than a threshold value.

In the pulse wave detecting device herein disclosed, the rotation angledetermining section performs processing for successively determining, asa target element, one element positioned on the artery from the pressuredetecting elements included in the element rows based on a group ofpressure signals detected by the respective pressure detecting elementsof the element rows during increase of a pressing force applied to thesensor section against the body surface by the pressing section, anddetermines the specific value in a state where the sensor section ispressed against the body surface with an arbitrary specific pressingforce with which an AC component of a pressure signal detected by thetarget element successively determining in one element row out of thetwo element rows has a value as large as 0.9 times or more of a maximumvalue of the AC component.

In the pulse wave detecting device herein disclosed, the rotation angledetermining section defines, as the first pressure detecting element andthe second pressure detecting element, target elements respectivelydetermined from the two element rows in a state where the pressing forceis the specific pressing force during the increase.

A vital information measuring device herein disclosed includes: theabove described pulse wave detecting device; and a vital informationcalculating section that calculates vital information based on thepressure signals stored in the storage medium.

A method for controlling a pulse wave detecting device herein disclosedis a method for controlling a pulse wave detecting device including: asensor section that includes at least one pair of pressure detectingelements arranged in a direction perpendicular to a first direction; apressing section that presses the sensor section against a body surfaceof a living body in a state where the first direction crosses adirection of an artery extending below the body surface; and a rotationdrive section that rotates the sensor section about an axis extending inthe first direction, the method includes: a storage control step ofstoring, in a storage medium, pressure signals detected by the pressuredetecting elements in a state where a rotation angle of the sensorsection about the axis is controlled to a specific value and the sensorsection is pressed against the body surface by the pressing section; anda rotation angle determining step of determining the specific valuebased on DC components of pressure signals detected, in a state wherethe sensor section is pressed against the body surface by the pressingsection, respectively by a first pressure detecting element and a secondpressure detecting element out of the pressure detecting elementsincluded in the sensor section, the first pressure detecting element andthe second pressure detecting element being different from each other ina position in the direction perpendicular to the first direction.

A control program for a pulse wave detecting device herein disclosed isa control program for a pulse wave detecting device including: a sensorsection that includes at least one pair of pressure detecting elementsarranged in a direction perpendicular to a first direction; a pressingsection that presses the sensor section against a body surface of aliving body in a state where the first direction crosses a direction ofan artery extending below the body surface; and a rotation drive sectionthat rotates the sensor section about an axis extending in the firstdirection, the control program causes a computer to execute: a storagecontrol step of storing, in a storage medium, pressure signals detectedby the pressure detecting elements in a state where a rotation angle ofthe sensor section about the axis is controlled to a specific value andthe sensor section is pressed against the body surface by the pressingsection; and a rotation angle determining step of determining thespecific value based on DC components of pressure signals detected, in astate where the sensor section is pressed against the body surface bythe pressing section, respectively by a first pressure detecting elementand a second pressure detecting element out of the pressure detectingelements included in the sensor section, the first pressure detectingelement and the second pressure detecting element being different fromeach other in a position in the direction perpendicular to the firstdirection.

The present invention is highly conveniently and effectively applied toa sphygmomanometer in particular.

According to the present invention, a pulse wave detecting devicecapable improving pulse wave detection accuracy by flexibly changing apressing state, toward a body surface, of a sensor section pressedagainst the body surface for use, a vital information measuring device,a control method for a pulse wave detecting device, and a controlprogram for a pulse wave detecting device can be provided.

The present invention has been described so far with reference to aspecific embodiment, and it is noted that the present invention is notlimited to the embodiment but can be variously modified withoutdeparting from the technical spirit of the present invention disclosedherein.

What is claimed is:
 1. A pulse wave detecting device, comprising: asensor section that includes at least one pair of pressure detectingelements arranged in a direction perpendicular to a first direction; apressing section that presses the sensor section against a body surfaceof a living body in a state where the first direction crosses adirection of an artery extending below the body surface; a rotationdrive section that rotates the sensor section about an axis extending inthe first direction; a storage control section that stores, in a storagemedium, pressure signals detected by the pressure detecting elements ina state where a rotation angle of the sensor section about the axis iscontrolled to a specific value and the sensor section is pressed againstthe body surface by the pressing section; and a rotation angledetermining section that determines the specific value based on DCcomponents of pressure signals detected, in a state where the sensorsection is pressed against the body surface by the pressing section,respectively by a first pressure detecting element and a second pressuredetecting element out of the pressure detecting elements included in thesensor section, the first pressure detecting element and the secondpressure detecting element being different from each other in a positionin the direction perpendicular to the first direction.
 2. The pulse wavedetecting device according to claim 1, wherein the rotation angledetermining section determines, as the specific value, a value of therotation angle with which a difference between the DC component of thepressure signal detected by the first pressure detecting element and theDC component of the pressure signal detected by the second pressuredetecting element is the minimum.
 3. The pulse wave detecting deviceaccording to claim 1, wherein the sensor section includes two elementrows each including a plurality of pressure detecting elements arrangedin the first direction, the two element rows being arranged in thedirection perpendicular to the first direction, pressure detectingelements disposed in the same position in the first directionrespectively in the two element rows together form the pair, and therotation angle determining section selects, as the first pressuredetecting element, one of the plurality of pressure detecting elementsincluded in a first element row out of the two element rows based on agroup of pressure signals detected by the pressure detecting elements ofthe first element row, and selects, as the second pressure detectingelement, one of the plurality of pressure detecting elements included ina second element row out of the two element rows based on a group ofpressure signals detected by the pressure detecting elements of thesecond element row.
 4. The pulse wave detecting device according toclaim 3, wherein the rotation angle determining section performsprocessing for successively determining, as a target element, oneelement positioned on the artery from the pressure detecting elementsincluded in the element rows based on a group of pressure signalsdetected by the respective pressure detecting elements of the elementrows during increase of a pressing force applied to the sensor sectionagainst the body surface by the pressing section, and determines thespecific value in a state where the sensor section is pressed againstthe body surface with a specific pressing force with which variation ofa DC component of a pressure signal detected by the target elementsuccessively determined in one element row out of the two element rowsis equal to or lower than a threshold value.
 5. The pulse wave detectingdevice according to claim 3, wherein the rotation angle determiningsection performs processing for successively determining, as a targetelement, one element positioned on the artery from the pressuredetecting elements included in the element rows based on a group ofpressure signals detected by the respective pressure detecting elementsof the element rows during increase of a pressing force applied to thesensor section against the body surface by the pressing section, anddetermines the specific value in a state where the sensor section ispressed against the body surface with an arbitrary specific pressingforce with which an AC component of a pressure signal detected by thetarget element successively determining in one element row out of thetwo element rows has a value as large as 0.9 times or more of a maximumvalue of the AC component.
 6. The pulse wave detecting device accordingto claim 4, wherein the rotation angle determining section defines, asthe first pressure detecting element and the second pressure detectingelement, target elements respectively determined from the two elementrows in a state where the pressing force is the specific pressing forceduring the increase.
 7. A vital information measuring device,comprising: the pulse wave detecting device according to claim 1; and avital information calculating section that calculates vital informationbased on the pressure signals stored in the storage medium.
 8. A methodfor controlling a pulse wave detecting device, the pulse wave detectingdevice including: a sensor section that includes at least one pair ofpressure detecting elements arranged in a direction perpendicular to afirst direction; a pressing section that presses the sensor sectionagainst a body surface of a living body in a state where the firstdirection crosses a direction of an artery extending below the bodysurface; and a rotation drive section that rotates the sensor sectionabout an axis extending in the first direction, the method comprising: astorage control step of storing, in a storage medium, pressure signalsdetected by the pressure detecting elements in a state where a rotationangle of the sensor section about the axis is controlled to a specificvalue and the sensor section is pressed against the body surface by thepressing section; and a rotation angle determining step of determiningthe specific value based on DC components of pressure signals detected,in a state where the sensor section is pressed against the body surfaceby the pressing section, respectively by a first pressure detectingelement and a second pressure detecting element out of the pressuredetecting elements included in the sensor section, the first pressuredetecting element and the second pressure detecting element beingdifferent from each other in a position in the direction perpendicularto the first direction.
 9. A non-transitory computer-readable storagemedium, which stores a control program for a pulse wave detectingdevice, the pulse wave detecting device including: a sensor section thatincludes at least one pair of pressure detecting elements arranged in adirection perpendicular to a first direction; a pressing section thatpresses the sensor section against a body surface of a living body in astate where the first direction crosses a direction of an arteryextending below the body surface; and a rotation drive section thatrotates the sensor section about an axis extending in the firstdirection, the control program causing a computer to execute: a storagecontrol step of storing, in a storage medium, pressure signals detectedby the pressure detecting elements in a state where a rotation angle ofthe sensor section about the axis is controlled to a specific value andthe sensor section is pressed against the body surface by the pressingsection; and a rotation angle determining step of determining thespecific value based on DC components of pressure signals detected, in astate where the sensor section is pressed against the body surface bythe pressing section, respectively by a first pressure detecting elementand a second pressure detecting element out of the pressure detectingelements included in the sensor section, the first pressure detectingelement and the second pressure detecting element being different fromeach other in a position in the direction perpendicular to the firstdirection.